Field of the Invention
The present invention relates to an image shake correcting apparatus for correcting image shake due to hand shake, and the like, and an imaging apparatus. In particular, the present invention relates to a technology for smoothly correcting image shake during macrophotography.
Description of the Related Art
With respect to a camera incorporating an image shake correcting apparatus, in order to enable photography without image shake, angular shake of the camera due to hand movement, or the like, is detected, and an image shake correcting lens (hereafter “correcting lens”) is driven in accordance with detection values. In this process, it is necessary to accurately detect camera shake and to correct changes in the optical axis due to shaking. Image shake is suppressed by a vibration detecting unit (angular velocity meter, or the like) that obtains detection results, such as angular velocity, and a drive control unit that drives a correcting member (correcting lens, or the like) based on calculating processing results.
Incidentally, in the case of close range photography (an imaging condition of high imaging magnification), there is shake that cannot be detected by an angular velocity meter alone. This is so-called translational shake that is applied in a direction parallel to or vertical to the optical axis of the camera, and image degradation caused thereby cannot be ignored. For example, under conditions when imaging is performed by approaching to within 20 cm of the subject in macrophotography, or when the focal distance of the imaging optical system is extremely large (e.g., 400 mm) relative to a subject that is at a distance of 1 m from the camera, it is necessary to actively detect translational shake and to perform correction.
Japanese Patent Laid-Open No. H7-225405 discloses a technology that translational shake is detected by an acceleration meter, the translational shake is obtained from second order integration of the acceleration meter, and a shake correction unit is driven in accordance with an output of a separately provided angular velocity meter. In this case, the output of the acceleration meter tends to be affected by environmental change, such as external noise or temperature variation, further increasing factors of instability due to second order integration, and thereby inhibiting highly accurate correction of translational shake. Japanese Patent Laid-Open No. 2010-25962 discloses a technology that translational shake is obtained by considering the translational shake as angular shake, when the center of rotation is located away from the camera. An angle and a correction value using a rotation radius of angular shake are obtained from the respective outputs of an angular velocity meter and an acceleration meter, and shake correction is performed. By obtaining a center of rotation by restriction to a frequency range that tends to be unaffected by external disturbances, the effects on correction from factors of instability of the acceleration meter can be mitigated.
Generally, if a cutoff frequency of a filter used in image shake correction is set low and if the frequency range is broadened, it is possible to improve performance by performing shake correction of low-frequency components with respect to movement of the body of a photographer, or the like. However, when the frequency range on the low-frequency side of the filter is expanded, the possibility conversely arises that performance will deteriorate, because the position of the correcting member reaches the limit of a movable range, given that the correcting member has a limited movable range.
Moreover, with the translational shake correction using a rotation radius disclosed in Japanese Patent Laid-Open No. 2010-25962, it is difficult to accurately perform correction in a low-frequency range. With respect to the rotation radius, the rotation radius is specified in a predetermined frequency range for calculation, and the extracted frequency is mainly set to between 1 Hz and 10 Hz. Consequently, with respect to shake of 1 Hz or less, it may happen that a rotation radius cannot be accurately obtained. Moreover, in the case when an actual rotation radius with a shake of 1 Hz, or less, is less than the rotation radius obtained by calculating operations, excessive shake correction that differs from actual translational shake may occur with respect to correction in a low-frequency range of 1 Hz or less. Under the foregoing conditions, it is to be feared that image shake correction performance will decline due to excessive correction associated with expansion of the frequency range on the low-frequency side of the filter.